The production of elastomeric materials is well described in the art. (See for example Kirk-Othmer Encyclopedia of Chemical Technology, 4th edition, volume 10, John Wiley & Sons, Inc., New York, 1993, pp.624-638.) Elastomeric materials, specifically spandex, contain urethane linkages with the following repeat structure:
Most urethane polymers in current use for the manufacture of spandex are made by reacting hydroxy-terminated polyethers or polyesters with a diisocyanate at a molar ratio of about 1:1.4 to 1:2.5, followed by reaction of the resulting isocyanate-terminated prepolymer with one or more diamines to produce a high molecular weight urethane polymer. Small amounts of monofunctional amines may also be included to control polymer molecular weight. Mechanical properties may be affected by changing the particular polyester or polyether glycol, diisocyanate, diamine(s), and monoamine used; they can be further modified by changing the molecular weight of the glycol and by changing the glycol-diisocyanate molar ratio.
The long-chain urethane polymer molecules in spandex are substantially linear block copolymers comprising relatively long blocks in which molecular interactions are weak, interconnected by shorter blocks in which interactions are strong. The weakly interacting blocks, commonly referred to as soft segments, are from the polyether or polyester glycol component whereas the blocks having strong interactions result from diisocyanate and chain extender reactions and are referred to as hard segments. The chain extension reaction is usually a coupling reaction between the isocyanate and difunctional amines, resulting in a urea linkage. Thus, the resulting polymer of the combined hard- and soft-segments are known as polyureaurethane.
It is known that polyisocyanate polymers can be used to prepare aqueous polyurethane dispersions. Polyurethane dispersions are generally prepared by chain extending the reaction product of an organic diisocyanate or polyisocyanate and an organic compound having two or more active hydrogen atoms such as polyalkylene ether glycols, poly(alkylene ether) glycols, alkyd resins, polyesters and polyester amides, often using a small amount of an organic solvent. The diisocyanate is used in stoichiometric excess so that the reaction product, also referred to as a polyurethane/urea prepolymer, is isocyanate terminated. Examples of polyurethane prepolymer preparations are described in U.S. Pat. Nos. 3,178,310, 3,919,173, 4,442,259, 4,444,976, and 4,742,095, among others.
Polyurethane dispersions are reported as being useful for preparing such diverse materials as coatings and bonds in U.S. Pat. No. 4,292,226; flexible solvent barriers in U.S. Pat. No. 4,431,763; adhesives in U.S. Pat. No. 4,433,095; and films in U.S. Pat. No. 4,501,852. Films, or rather the process of dipping to make a film, can be a part of the processes for making many articles. Examples of film applications include gloves, organ bags, condoms, ostomy bags, and the like. While it is known that such applications can be made with polyurethane dispersions, conventional polyurethane dispersions have sometimes been found to have insufficient physical or handling properties to make them a preferred material for such applications. Also, the use of certain relatively high-boiling solvents, such as N-methyl-2-pyrrolidone, can have adverse effects for some applications.
Polyurethanes are the reaction product of a polyalcohol and a polyisocyanate. Typically, the polyisocyanates used to prepare aqueous polyurethane dispersions have been aliphatic isocyanates such as those disclosed in U.S. Pat. No. 5,494,960. Even though aromatic polyisocyanates such as toluene diisocyanate (TDI) and methylene diphenyldiisocyanate (MDI) as well as polymethylene polyphenylisocyanate (PMDI) are also known to be useful, the aliphatic isocyanate was found to have much higher stability toward hydrolysis while the prepolymer is dispersed in water. Thus, it is generally believed that the reaction between the isocyanate and the difunctional amine takes place in a more controlled and predictable manner.
Films prepared from natural rubber latex are common, but are considered to have properties which are desirable from the perspective of comfort and utility. Unfortunately, natural rubber latex also includes proteins and other materials, such as sulfur containing curing agents, which can be irritating to the skin, and which may cause severe allergic reactions in some people.
PCT International Application No. WO 00/61651, published Oct. 19, 2000, discloses polyurethane films and dispersions for their preparation. The dispersion is prepared from a polyurethane prepolymer formulation including a diisocyanate and an active hydrogen containing material. The dispersion is formed in a two or more step process wherein, in a first step, the prepolymer is formed and, in a subsequent step, an aqueous dispersion of the prepolymer is formed, in the presence of an anionic surfactant, both steps occurring in the substantial absence of an organic solvent.
Elastic films with good moisture management can provide protection from the environment, such as germs and chemicals. Particularly with the increased potential threat from chemical and biological agents, the need of such materials is ever increasing. Recent incidents has shown need for a comfortable gloves, which can be worn by law enforcement and postal workers for a long period of time. Latex gloves usually have low puncture resistance, and moreover may pose additional health risks, including fatal allergic reactions by certain individuals. Nitrile gloves have good puncture resistance, but high modulus, so they can cause fatigue with long term use.
Polyurethane elastomers may offer an alternative material choice, but some of polyurethane gloves are found to get weak when it is exposed to water or rubbing alcohol. This would hinder the long term use of such gloves.
We have found that by carefully formulating a polyurethane, gloves with many desired properties could be obtained.